While the burning of a candle might appear to be simple and uninvolved, in fact, the process that takes place in the burning of a candle imposes rather stringent requirements upon the candle body material. At the outset, a typical wax candle body must be rigid enough to support itself (or be supported), in a relatively long wick filament, but it should not be excessively brittle at low room temperatures.
With respect to the actual burning of the candle, the heat of the candle's flame melts a small pool of the candle body material around the base of the exposed portion of the wick, and this molten material is then drawn up through and along the wick by capillary attraction, to fuel the flame. A candle's melting point is critical, in that the candle material should liquefy at or below temperatures to which the candle's material can be raised by radiant heat from the candle flame. If the candle's melting temperature is too low, the candle will drip or, in an extreme case, the entire candle body will melt, dropping the wick into a pool of molten body material, with the potential that the surface of the pool could ignite. If too high a temperature is required to melt the body material, the flame will be starved because insufficient fuel will be drawn up through the wick, with the result that the flame will be too small to maintain itself. Moreover, when molten, the candle body material must have a relatively low viscosity to insure that it will be capable of being drawn up through the wick by capillary action. In addition to meeting the above requirements, it is preferred that the candle body material burn with a flame that is both luminous and smokeless, and the odors that are produced by its combustion should not be unpleasant or intrusive.
Heretofore no composition that meets all these requirements has been transparent or clear (the terms "clear" and "transparent" are used interchangeably herein and connote a substantial absence of cloudiness/obscurity, so that the product features an ability to let light pass through in a substantially unobstructed manner, and an ability to have colorant added to the composition without the loss of the absence of cloudiness/obscurity or of the ability to let light pass through in a fairly unobstructed manner). Although clear candles have been disclosed in the prior art, none of these formulations have fulfilled all of the above described requirements of a candle in general, nor have they possessed all of the benefits of the clear candle of this invention. The present invention has an objective of providing a clear candle with a soft rubbery consistency which does not change or harden, and which possesses all of the necessary characteristics of a candle and which, moreover, is truly transparent.
The candle body of this invention is made by the physical cross linking of copolymers to form a gel which is heterophase ("heterophase" as used herein means a 2-phase system, which comprises an "oil" phase and a "block co-polymer" phase, the two phases being separate chemically and on a micro scale physically, but indistinct on a macro scale physically), and thermally reversible (i.e., when the gel is heated, the chemical composition of the gel remains the same, only physical properties of the gel--such as viscosity--change). The clear candles disclosed in the prior art are typically manufactured with a thermoplastic polyamide resin which requires a chemical reaction to solidify the gel. The polyamide resin materials of these prior candles, when heated, melt into and form chemical substances different from the original monomers or chemical constituents. Thus, these polyamide resin based clear candles are not thermally reversible.
A characteristic polyamide resin based candle is disclosed in U.S. Pat. No. 3,819,342 ("the '342 patent"). This patent discloses a transparent candle composition comprising a thermal plastic polyamide resin and a flammable solvent described as being capable of solubilizing the resin at a temperature below about 212.degree. F., and forming a transparent gel-type structure. The solvent of the '342 patent is selected from the group consisting of unsaturated fatty acids, unsaturated fatty alcohols, saturated fatty alcohols, esters of fatty acids with polyhydric alcohols and glycerol, and mixtures thereof, and being present in amounts sufficient to gel the resin. Additional materials used in this candle are coloring, anti-flaring compounds, perfumes, clarifying agents. Examples of different anti-flaring compounds are listed, however, the requirement of an anti-flaring compound points out a most serious problem with all polyamide resin based candles. Specifically, polyamide resins are known to separate into layers, and, after separation, the top of the candle is covered with an oil layer that flashes when lit. This flashing can obviously be hazardous and is functionally inconsistent with a candle's natural function of providing reliable, consistent lighting. Clear candles made in accordance with this invention have the advantage of being completely stable over time. They will not separate into layers as prior art candles would, and thus there is no excess fluid available to flash.
U.S. Pat. No. 3,615,289 ("the '289 patent"), discloses another clear candle that is chemically very similar to the devices of the '342 patent discussed above. The '289 patent discloses a candle composition which may be transparent or pastel shaded and which is allegedly adapted to incorporate perfumes without flashing during burning. The basic composition of the '289 patent comprises a thermoplastic polyamide resin formed from linoleic acid polymerized with polyamide compound; an alkolamide or alkanol; and a stearic acid compound. The '289 patent further describes the use of polyamide resins to allegedly help eliminate "sweating" and to provide a smoother and glossier finish. Sweating is the process whereby oils migrate out of the candle body to the surface, giving it a oily texture, and is most commonly caused by syneresis. Syneresis occurs when oil is physically squeezed out from the candle body because of excessive chemical crosslinking. Sweating is not only an aesthetic drawback, it can be a performance or safety problem as well. If a candle sweats, the oil on the surface is available to ignite, which can result in an uncontrolled or torch-like situation rather than a candle.
Practical experience with, and laboratory testing of, the '289 and '342 candles has indicated that separation was a consistent and serious problem. Sweating also occurred in these candles, but the amount of oil secreted was small with respect to the large pool of oil that forms on the top of the candles after phase separation. The gel based candle of the present invention does not sweat or separate, because syneresis can be easily controlled by adjusting the ratio of diblock to triblock polymers to insure that all of the oil is entrained within a system of physically crosslinked copolymers.
The '289 patent also discusses the optional addition of ionic surface agents to prevent "blooming" or fogging of the candle which would result in the loss of transparency. This is significant because another persistent complaint about commercially available polyamide resin based candles is that they are initially cloudy or they become cloudy over time. The addition of the ionic surface agents may help this problem in some cases, but it does not eliminate cloudiness in the polyamide resin based candles. In stark contrast, candle's made according to this invention start out clear, remain clear during burning, and do not "bloom" or fog over time.
U.S. Pat. No. 3,645,705 discloses a transparent candle body material formed by combining a straight chain aliphatic amide with white mineral oil and alcohol. The '705 material is therefore, polyamide resin based, and is described as providing a molded, solid, and free standing product. The resin is mixed with natural oils to cause it to gel. This invention claims to be transparent as glass but slightly yellow due to the oil content. There is also a methyl ester added for hardness. The '705 patent is, however, similar in composition to the '342 and '289 patents and has the same structural and functional problems associated with it, and is therefore chemically as well as physically distinct from the present invention.
U.S. Pat. No. 3,741,711 ("the '711 patent"), discloses a clear, undyed and unpigmented wax based "candle." However, a closer reading of this patent indicates that the invention is a reusable "candle holder" and not a "candle". Particularly, the '711 patent discloses a multilayer holder with a decorated outer surface. The disclosure further states that the candle body has "an illuminous glow throughout the body of the candle . . . when the candle is being burned." There are, however, no compositions claimed, or disclosed, other than wax. In this particular patent, "clear" apparently means, a wax that is undyed and unpigmented. The lack of pigment and/or dye is referred to numerous times in the disclosure, but there is no disclosure that the wax used is any different than the opaque paraffin wax used in normal candle making. In contrast, the clear candle of the present invention is a true candle that bums and is consumed, and it is not a wax based candle but rather a gel based system of physically crosslinked copolymers.
Thus, in general, the clear candle of this application addresses and overcomes the structural, aesthetic and functional problems of prior art candles by providing a gel body of the present invention is formed by physically crosslinked block copolymers in a heterophase thermally reversible mineral oil gel. The paraffin wax or polyamide thermoplastic resin products known heretofore cannot provide a stable, clear candle having the structural and performance advantages as set forth herein.
PCT Application No. WO 88-00603 ("the '603 publication"), published Jan. 28, 1988, describes block copolymers which can be advantageously used as one or more components in the present invention. These block copolymers are described as gels or gelloid liquid extended polymer compositions which can comprise an intimate mixture of a block copolymer containing relatively hard blocks and relatively elastomeric blocks. The additional polymer or copolymer material of this disclosure is to have at least partial compatibility with and a higher glass transition softening or melting temperature than the hard blocks of the block copolymer, and at least 500 parts by weight of extender liquid per 100 parts of the block copolymer, the liquid being present to extend and soften the elastomeric blocks of the block copolymer. The extender liquid can be a hydrocarbon oil and/or a synthetic oil and the resulting gels or gelloid compositions are of the type which can be used in the clear candle of the present invention. However, there is no teaching, or suggestion in the '603 publication of the potential for using these materials in a candle, let alone to form a clear candle. The '603 publication is hereby incorporated by reference herein.
Similarly, gel material as described in U.S. Pat. No. 5,221,534 ("the '534 patent") can also be utilized as the gel material for the body of the candle of the present invention. The '534 patent describes a health and beauty aid gel composition comprised of one or more health and beauty aid components, a mineral oil, and a blend of at least two different polymer members. The viscous, yet flowable material of the '534 patent was initially contemplated by the present applicant as a potential additive for standard wax based candles to enhance quality and to make them softer and less brittle, because the material of the '534 patent does not coke during burning. As a candle burns down into a container there may be insufficient oxygen at the bottom of the container to support complete combustion. Particles of incomplete combustion (known as soot or coke) can thereby form on the upper inside edge of the container; coking typically takes the form of a black smudge-like ring around the top of the container. During testing, however, it was observed that the material of the '534 patent began to separate into layers when it sat for a short period of time. Also, the material flashed when the wick placed in it was lit. These characteristics made this material unsuitable for the purpose of a candle additive.
During testing however, a reformulated, more gel-like version of the material of the '534 patent was checked for possible use as an additive. The amount of the triblock polymers was increased so as to make the material more gel-like. While the product was determined to be of no interest as a candle additive, the testing led to an important discovery. The reformulated material was heated until it flowed, it was poured into a jar. A wick was then placed into it, and the sample was burned. There was no separation into phases, no sweating, and the material did not flash when burned. Surprisingly and quite unexpectedly, it was discovered that the experimental candle was transparent, it's body glowed when lit, and it did not discolor upon burning. The transparent nature of the candle made it extremely attractive.
Although this reformulated version of the '534 patent forms an excellent clear candle, it is at the same time rendered less suitable for its original purpose as a carrier for health and beauty aid compositions because of its gel (semi-solid) form. Importantly, there is no teaching or suggestion in the '534 patent of the potential for using this material as a candle. The disclosure of the '534 patent is hereby incorporated herein by reference.